<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <link href="table.css" rel="stylesheet" type="text/css">
</head>
<body >
  <table id="tb">
      <tr>
          <th>姓名</th>
          <th>年龄</th>
          <th>性别</th>
      </tr>
      <tr class="alt">
          <td>小王</td>
          <td>20</td>
          <td>男</td>
      </tr>
      <tr>
          <td>小王</td>
          <td>20</td>
          <td>男</td>
      </tr>
      <tr class="alt">
          <td>小王</td>
          <td>20</td>
          <td>男</td>
      </tr>

  </table>
</body>
</html>